Fluid system

ABSTRACT

A fluid system having a variable displacement fluid pump connected in a closed loop circuit to a fluid cylinder having a piston and a pair of connecting rods extending from opposite sides of the piston externally of the fluid cylinder. A directional control valve disposed in the closed circuit between the inlet and outlet of the fluid pump is adapted to selectively direct fluid to one side of the piston within the fluid cylinder, while exhausting fluid from the other side of the piston, to selectively move the piston within the fluid cylinder. The rate of movement of the piston in either direction of movement is controlled by the amount of fluid displaced by the fluid pump. A second directional control valve is adapted to direct fluid from a second source of fluid to a pressure responsive displacement control mechanism to selectively vary the displacement of the fluid pump between a maximum and a minimum flow position. The rate of fluid flow to the pressure responsive displacement control mechanism is selectively varied to control the rate of displacement of the fluid pump and to thereby selectively control the rate of movement of the cylinder piston, while the maximum flow position may be varied between defined limits by an electrically operated remote control.

United States Patent Kllbik Oct. 24, 1972 [54] FLUID SYSTEM 72 Inventor:Philip A. Kubik, 6809 Spruce Drive, [57] ABSTRACT Birmi gh MiCh- A fluidsystem having a variable displacement fluid [22] Filed: 26, 1970 pumpconnected in a closed loop circuit to a fluid Appl. No.: 67,177

Related US. Application Data Primary Examiner-William L. FreehAttorney-Andrew R. Basile cylinder having a piston and a pair ofconnecting rods extending from opposite sides of "the piston externallyof the fluid cylinder. A directional control valve disposed in theclosed circuit between the inlet and outlet of the fluid pump is adaptedto selectively direct fluid to one side of the piston within the fluidcylinder, while exhausting fluid from the other side of the piston, toselectively move the piston within the fluid cylinder. The rate ofmovement of the piston in either direction of movement is controlled bythe amount of fluid displaced by the fluid pump.

17 Claims, 12 Drawing Figures PATENTED act 24 m2 SHEET 1 OF 3 INIVENTORPHILIP A. KUBIK l //%zm 1 I WW ATTORN EYS PATENTEDHBI 24 1912 '3. 70035s SHEET 2 OF 3 FIGS INVENTOR PHILIP A. KUBIK BY ,fiM /fW @12445ATTORNEYS FIGIO PATENTEDUCT 24 I972 3,700,356

SHEET 3 0F 3 FIG.6

FIG 7 F|G.9 [MW/Q l INVENTOR I PHILIP A- KUBIK 24v 202 BY %ae,

ATTORNEYS FLUID SYSTEM CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of application Ser. No. 50,093,filed June 26, 1970 and now US. Pat. No. 3,653,208.

BACKGROUND OF THE INVENTION ployed for controlling the rate of movementof a hydraulic motor and, particularly, such fluid systems have foundextensive use in hydraulic machine tool drive transfer systems and thelike. Such fluid systems are used to accelerate and decelerate a fluidcylinder respectively at the beginning and the end of its stroke priorto a feed movement. Such previously used fluid systems have normallyconsisted of a reservoir and a fluid pump for drawing fluid from thereservoir to supply the fluid cylinder and drive the same at someselected rate of movement. Suitable valving means are employed betweenthe pump and the fluid cylinder to control the rate of movement of thefluid cylinder. The rate of movement of the fluid cylinder is asignificant factor which must be considered in all but the simplest ofcircuits. When a variable rate control of the fluid cylinder is desired,it is customary to employ a meterin, meter-out, or a bleed-off system.Such systems generally include a deceleration valve connected in serieswith the pump; the deceleration valve being actuated by the movement ofthe fluid cylinder to variably restrict or stop the fluid flow betweenthe outlet of the pump and the inlet of the fluid cylinder. When a finerrate control isdesired, a feed control valve connected in parallel withthe deceleration valve is utilized. The feed control valve, which may beof the meter-in or meter-out type, controls the rate of flow to or fromthe fluid cylinder and may either be a fine or coarse feed, depending onthe desired application. If the feed control is of the meter-in type,the rate of fluid flow supplied to the fluid cylinder is controlled. Ifthe fluid flow from thedevice is controlled, the circuit is known as ameter-out circuit. When a portion of the fluid supply is diverted to areservoir, the circuit is known as a bleedoff circuit. 7

Thus, in the previously used systems, fluid flows directly from the pumpthrough a deceleration valve, a feed control valve and to the fluidcylinder. In such systems, if the load greatly varies, the feed controlvalves require pressure compensation.

Such systems, although commonly used, are difficult to adjust andcontrol and, because of the pressune compensation required for variableloads, they have a lower efflciency than is desirable. Sinceacceleration and deceleration of the fluid cylinder is accomplished bymeans of a deceleration valve, such acceleration and deceleration is notsmooth as the deceleration valves tend to generate pulsations in thefluid system which can damage the fluid cylinder and/or the fluid pump.Further, braking of the fluid cylinder is not obtainable as suchpreviously used fluid systems are not a closedloop system. In addition,such systems are not capable of having a controlled acceleration,deceleration, start and stop at present rates, while having a means forchanging the maximum output speed from a remote control position.

It would therefore be desirable to provide a fluid system which has allthe advantages of the heretofore previously used systems without any ofthe aforementioned disadvantages.

SUMMARY OF THE INVENTION The present invention, which will be describedsubsequently in greater detail, comprises a fluid system having aclosed-loop fluid circuit for selectively connecting the inlet andoutlet of a main fluid motor to the inlet and outlet of a fluid pump.The main fluid motor may be a fluid cylinder of the type having a pistonwith connecting rods extending from the opposite sides thereof andexternally of the main fluid cylinder, whereby the effective pressureresponsive areas on the opposite sides of the main cylinder piston areequal. The pump has means for varying its displacement between minimumand maximum flow positions and is controlled by a fluid circuit having asecondary fluid cylinder which is operatively connected to thedisplacement varying means of the pump. The piston in the secondaryfluid cylinder has its opposite sides selectively connected to a sourceof fluid through a pair of feed control valves and a conventionaldirectional control valve. The acceleration and deceleration of thepiston in the main fluid cylinder is controlled by varying thedisplacement of the fluid pump, which, in turn, is controlled by thefeed circuit. An electrically operated remote control means is providedfor varying the maximum flow position of the pump within preset limitsto enable a change in the maximum output speed of the fluid motorwithout affecting preset rates of starting,

acceleration, deceleration, and stopping of the fluid motor.

It is therefore an object of the present invention to provide a fluidsystem for controlling the rate of movement of a fluid motor which iseasily adjustable from a remote location and controlled more efficientlythan previously used control circuits.

It is also an object of the present invention to provide a fluid systemfor controlling the rate of movement of a fluid pump control circuit inwhich the acceleration and deceleration forces exerted on a fluid motorare smooth.

It is also an object of the present invention to provide a fluid systemin which the maximum output speed may be varied remotely between presetlimits without affecting other control characteristics of the system.

It is also an object of the present invention to provide means forvarying the maximum and/or minimum displacement of a variabledisplacement fluid pump between preset limits.

Other objects, advantages, and applications of the present inventionwill become apparent to those skilled in the art of fluid systems andfluid pumps when the accompanying description of several examples of thebest modes contemplated for practicing the invention is read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The description herein makes referenceto the accompanying drawings in which like reference numerals refer tolike parts throughout the several Figures, and in which:

FIG. 1 represents a schematic illustration of the present invention inthe form of a fluid system;

FIG. 2 is a schematic illustration of a modification of a fluid pumpillustrated in FIG. 1;

FIG. 2A is a rear elevational view of the fluid pump illustrated in'FIG.2 as seen from line 2A-2A;

FIG. 3 is an enlarged fragmentary, partially sectioned top plane view ofthe fluid pump illustrated in FIG. 2 as seen from line 3-3;

FIG. 4 is a schematic illustration of another modification of the fluidpump illustrated in FIG. 1 taken in cross-section along line 4-4 of FIG.4A;

FIG. 4A is a front elevational view of the fluid pump illustrated inFIG. 4 as seen from line 4A4A;

FIG. 5 is an enlarged fragmentary cross-sectional view of the fluid pumpillustrated in FIG. 4;

FIG. 6 is an enlarged fragmentary cross-sectional view of the fluid pumpillustrated in FIG. 4A and taken on line 6-6;

FIG. 7 is a fragmentary cross-sectional view of FIG. 6 taken generallyalong line 77 thereof;

FIG. 8 is a schematic illustration of a third modification of the fluidpump illustrated in FIG. 1;

FIG. 9 is an enlarged fragmentary cross-sectional view of FIG. 8; and,

FIG. 10 is a schematic diagram of one example of an electricallyoperated remote control circuit incorporating features of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings,there is illustrated a fluid system 10 comprising a control circuit 12and a main circuit 14. The main circuit 14 comprises a variabledisplacement pump 16 connected in closed-loop manner by conduits 18, 20,22 and 24 to a main fluid cylinder 26. Incorporated in the main circuit14 is a conventional directional control valve 28 which is adapted toconnect the conduits l8 and 20 selectively to the conduits 22 and 24 orbe positioned tandem-center so as to allow communication betweenconduits 18 and 20, but prevent fluid communication between conduits 22and 24.

The pump 16 may be of the well known axial piston type, comprising ahousing 30 having a cylindrical barrel 32 rotatably mounted therein andsuitably connected to a drive shaft 34. The cylinder barrel 32 is formedwith a plurality of axial cylinder bores each housing a pistonreciprocal therein; only two of the bores and pistons being shown andrespectively indicated by the numerals 36 and 38. Each piston 38 has aspherical outer end portion 40 carrying a bearing shoe 42 that engages aswash plate 44 which is operatively coupled to a secondary fluidcylinder 46 by a connecting arm 48 for movement about a pivot 50 from aneutral, minimum displacement position 52 to a maximum or full flowposition 54. A prime mover, such as an electric motor schematicallyillustrated at 56, is mechanically connected through a suitable couplingto the drive shaft 34 which, in turn, is supported within the pumphousing 30 by bearings 58 and 60.

As is conventional in pumps of the type illustrated, each cylinder bore36 in the cylinder barrel 32 is provided with a cylinder port 62 adaptedto alternately register with the inlet and outlet ports 64 and 66respectively as the cylinder barrel 32 rotates. The inlet and outletports 64 and 66 respectively communicate with the conduits l8 and 20.

The cylinder barrel 32, pistons 38, swash plate 44, and the input shaft34 are immersed in fluid in a filled cavity normally referred to as apump case 68. The pump 30 communicates with a reservoir 70 through acharge pump 92 and valving 100 or 102 and a conduit 94 on inlet and aconduit 72 on drain, all of which will be described hereinafter.

The main fluid cylinder 26 has a cylindrical housing 74 with an internalbore 76 in which a cylindrical piston 78 is reciprocally mounted,dividing the internal bore 76 into two pressure chambers 80 and 82respectively on the opposite sides of the piston 78. The opposite sidesof the piston 78 have cylinder rods 84 and 86 which extend through theopposite endwalls and externally of the main fluid cylinder 26. Thepressure chambers 80 and 82 of the cylinder 26 respectively have a fluidport 88 and 90 which, in turn, are respectively connected to the fluidconduits 22 and 24. Since the connecting rods 84 and 86 are of an equaldiameter, the eflective pressure responsive areas on the opposite sidesof the piston 78 are also equal. The cylinder 26 operates in a wellknown manner to move the piston 78 in opposite directions within thecylinder bore 76 when one of the pressure chambers 80 or 82 ispressurized, while the other pressure chamber is exhausted.

The fluid system 10 is provided with a positive fixed displacementreplenishing pump 92, such as a gear pump, which is also driven by theprime mover 56 through the drive shaft 34. The replenishing pump 92 isin communication with the reservoir 70 through a supply conduit 94 and afilter 96 for supplying the replenishing fluid to the main circuit 14 bymeans of a delivery conduit 98. Spring biased check valves 100 and 102are in communication with the delivery conduit 98 and the closed-loopmain circuit conduits 18 and 20, respectively, for supplyingreplenishing fluid to whichever of the conduits 18 and 20 is the lowpressure side of the closed main circuit through one of the checkvalves, which pressure on the high pressure side of the main circuitmaintains the other check valve closed.

A spring biased relief valve 104 is provided for the replenishing pump92 for relieving excessive fluid pressure in the replenishing deliveryconduit 98 for exhausting fluid to the reservoir 70 by means of a fluidconduit 106 connected to the pump case 68 and the conduit 72.

Downstream of the directional control valve 28, the conduits 22 and 24are respectively connected to the inlets of high pressure relief valves108 and l 10 which,

at a predetermined pressure, eg: 3,000 psi, will exhaust the fluidpressure from one of the conduits to the other conduit so as to preventdamage to the main circuit in the event of over pressurization.

Referring to the control circuit 12 for a description of the method ofcontrolling the displacement of the fluid pump 16, there is illustrateda directional control valve 112 adapted to selectively connect fluidfrom the replenish pump 92 to either of a pair of feed control valves114 and 116 by conduits 118 and 120 respectively. The feed valves 114and 116 are respectively connected to the ports 122 and 124 of thesecondary cylinder 46 bymeans of conduits 126 and 128 respectively. Thefluid cylinder 46 is similar in construction to the main cylinder 26 andcomprises a tubular housing 130 having an interior bore 132 divided intotwo pressure chambers 134 and 136 by means of a reciprocally mountedpiston l38,which, in turn, carries a connecting rod 140. Connecting rod140 extends externally of the housing 130 and is operatively coupled at142 to the swash plate connecting arm 48 of pump 16. The pressurechambers 134 and 136 are respectively connected to the conduits 126 and128.

The feed control valves 114 and 116 may be of the conventional type andhave restricted passages 144 and 146 which are adjustable such that eachof the feed control valves may be pre-set to supply any desired flowrate over a wide range. Each of the feed control valves 114 and 116includes a check valve 148 and 150, respectively, which permits fluid tobypass the restricted passages 144 and 146 in one direction. Thus, whenthe directional control valve 112 is in the position indicated, fluidflow is directed from the fixed displacement pump 92 through the conduit120 to the feed control valve 1 16, bypassing the same through checkvalve 150, and is then directed to the pressure chamber 136 on one sideof the cylinder piston 140 to move the same leftwardly within thecylinder bore 132 to displace the fluid pump 16 toward its full flowposition 54. Fluid on the opposite side of the piston cylinder 138within the pressure chamber 124 will be exhausted through the cylinderport 122 and directed through conduit 126 to the feed control valve 114at a rate of flow which is determined by the setting of the restrictedpassage 144. Fluid returns to the reservoir 70 through the directionalcontrol valve 112 and a conduit 152. When the directional control valve1 12 is reversed so as to direct fluid flow through the check valve 148of the feed control valve 1 14 to the pressure chamber 134 to move thepiston 138 rightwardly, fluid is exhausted through the restrictedpassage 146 of the feed control valve 116 which, in turn, controls therate of movement of the piston 138. As the piston 138 movesrightwardly,the swash plate connecting arm 48 is moved to the minimum displacementposition 52.

The type of feed control illustrated is known as a meter-out control,that is, the rate of movement of the piston 138 within the secondarycylinder 46 is determined by the rate of the fluid being exhausted fromthe pressure chamber 134 or 136, which, in turn, is controlled by thefeed control valves 114 and 116. A detailed description of the feedcontrol valves 114 and 1 16 is not necessary as such feed control valvesare well known and commercially available.

It can thus be seen that the rate of change in the displacement of thefluid pump 16 is controlled by the feed control valves 114 and 116,thus, if the restricted passages 144 and 146 of the feed control valvesare set to permit a high rate of flow to pass therethrough, the

6 cylinder piston 138 will be displaced rapidly causing a rapid changein the displacement of the fluid pump 16 which, in turn, whencommunicated to the main fluid cylinder 26 will generate a rapidacceleration and/or deceleration of the cylinder piston 78 therein.

The connecting rod carries a stop member 154 which is adapted to abutaxially adjustable mechanical stops 156 and 158 to permit a variation inthe displacement of the fluid pump 16 at predetermined intermediatedisplacements respectively below the maximum displacement of the fluidpump 16 and above the minimum displacement of the pump 16. The maximumdisplacement of the pump 16 occurs when the swash plate 44 abuts thewall 160 of the pump housing, while the minimum displacement of the pump16 occurs when the swash plate 44 is disposed in a plane which issubstantially perpendicular to the longitudinal axis of the drive shaftr In operation, when it is desired to direct fluid from the fluid pump10 through the conduit 18, the directional control valve 28 and theconduit 24 to ac celerate the piston 78 in the main cylinder 26forwardly (to the right as viewed in the drawings) at a rapid rate, thedirectional control valve 112 of the control circuit 12 is actuated byswitching means 162 to direct fluid from the fixed pump 92 into thepressure chamber 136 of the fluid cylinder 46 to drive the pistontherein rearwardly to stroke the swash plate 44 of the fluid pump 16 tothe maximum displacement 54 or some other intermediate displacement asdetermined by the setting of the adjustable stop 156. Fluid from thesecondary cylinder 46 is exhausted through the adjustable restrictedpassage 146 of the feed control valve 116 which is set to permit a highrate of fluid flow therethrough, thus permitting a rapid stroking of thepump 16 which, in turn, will displace a maximum amount of fluid into theconduit 18. The directional control valves 112 and 28 in the control andmain circuits, respectively, are simultaneously actuated so that as thesecondary cylinder 46 is actuated, fluid from the variable displacementpump 16 will be directed to the main fluid cylinder 26 to accelerate thepiston 78 thereinrapidly to the right as viewed in the drawings. Afterthe piston is displaced at a rapid rate of acceleration and strikes alimit switch Ll, the directional control valve 112 in the controlcircuit 12 is actuated, to direct fluid to the pressure chamber 136 onthe opposite side of the piston 138 in the secondary fluid cylinder 46.Fluid entering the secondary cylinder 46 will move the piston 138rightwardly to stroke swash plate 44 toward the minimum flow position 52or some intermediate displacement position determined by the adjustablestop 158. The fluid in the pressure chamber 134 of cylinder 46 will beexhausted through the feed control valve restricted passage 1414 at somepredetermined rate which will control the rate at which the piston 138of the fluid cylinder 46 strokes the pump 16 back towards a lowerdisplacement. As the pump 16 is stroked toward a lower displacement, therate at which fluid is directed to the main cylinder 26 is decreased,

thereby decelerating the movement of the piston 78.

within the main fluid cylinder 26. When the pump 16 is stroked to aminimum, the forward movement of the piston 78 of the main cylinder 26will be brought to a minimum creep speed to seek a final stop position,at

which time valve 28 will be centered and the piston will stop. Apositive stop 166 may be provided to insure that the cylinder piston 78stops at a desired position. The valve 28 may be actuated to a centeredposition by means of limit switch L2.

Acceleration and deceleration of the piston 78 within the main cylinder26 in an opposite direction (to the right as viewed in the drawings) maybe had by reversing the flow from the conduits 18 and 20 to the conduits22 and 24 by means of the directional control valve 28 without requiringany change in the setting of the feed control valves 114 and 116 as thevolume of fluid required to move the piston in either direction at somepredetermined rate is equal.

Moving the directional control valve 28 to a tandemcenter or no-flowcondition will prevent fluid flow either to or from the cylinderchambers 80 and 82, quickly stopping the piston 78. Such a quick stopmay be utilized in the event of an emergency when it is necessary toprevent damage to the machine tool or transfer mechanism which theconnecting rod 86 and/or 84 is driving.

Referring to FIG. 2, the pump 16 is illustrated in a modified form withthe swash plate 44 having a pair of diametrically opposed pintle shafts162 and 164 which are mounted to interior walls of the housing 30 bymeans of pintle bearings 166. The swash plate connecting arm 48 is inthe form of an L-shaped handle having a lower end extending through thewall of the pump housing 30 and operatively coupled to the pintle shaft164, as can be best seen in FIG. 2A. The upper end of the swash plateconnecting arm 48 extends through an elongated slot 167 (FIG. 3) formedin a bracket assembly 168 and is coupled to the connecting rod 140 ofthe secondary cylinder 46 at 142 in the same manner as describedhereinbefore. The adjustable mechanical stops 156 and 158 areillustrated in FIGS. 2 and 2A as being carried on the bracket assembly168 which, in turn, is attached to the housing of the pump 16. Themechanical stops 156 and 158 are disposed on opposite sides of the swashplate connecting arm 48 within its path of movement across the slot 167as the inclination of the swash plate 44 is varied. The mechanical stop158 may take the form of an adjusting screw 169 extending through amounting block 171 which is, in turn, fixedly attached to the bracket168. The screw 169 may be manually adjusted at a predeterminedintermediate position above the minimum displacement of the pump 16 suchthat when the secondary cylinder 46 is actuated to rotate the swashplate 44 to a minimum displacement position, the swash plate connectingarm 48 will abut the mechanical stop 158 at the desired minimumdisplacement position. Likewise, the mechanical stop member 156 may beremotely adjusted, in a manner which will be described hereinafter, to apredetermined intermediate position below the maximum displacement ofthe fluid pump 16 such that the swash plate connecting arm 48 will abutthe mechanical stop 156 at the desired maximum displacement position.

The mechanical stop 156 is carried at the end of an arm member 170 of anactuator 172 and is adapted to vary the position of the mechanical stop156 within a predetermined maximum displacement range. The end of thearm member 170 associated with the stop 156 has a threaded surface 173which is received in a threaded bore 175 in the stop 156. Since the stop156 is restrained from rotation, relative rotary motion between the armmember 170 and the stop 156 will cause axial movement of the stop 156.When the arm member 170 is actuated to shift the mechanical stop 156leftwardly, as viewed in FIGS. 2 and 3, the displacement of the pump 16will be increased as the swash plate 44 is rotated a greater amount fromits neutral position, resulting in an increased output of the pump 16and ultimately an increase in the speed of the fluid cylinder. If thearm member 170 is actuated to drive the mechanical stop 156 rightwardly,as viewed in FIGS. 2 and 3, the maximum displacement of the unit will bedecreased accordingly, as the swash plate connecting arm 48 will abutthe mechanical stop 156 after rotating a lesser amount from its neutralposition.

The actuator 172 is driven by an electric motor 174 (FIG. 2A) through apulley and belt arrangement 176 in a manner to be described in detailhereinafter.

The actuator 172 comprises a housing 178 (FIG. 3) having an internalbore 180 in which a hollow sleeve member 182 is rotatably mounted. Oneend of the sleeve member 182 projects outwardly from the rear of thehousing 178 and has a pulley 184 coupled thereon by a pin 186 extendingthrough both the pulley 184 and the projecting end of the sleeve 182.The interior of the sleeve member 182 has a threaded surface 188 whichreceives a mating threaded section 190 formed on the inner end of thearm member 170. Thrust bearing 189 provides a suitable bearing supportfor the rotating sleeve member 182.

It can thus be seen that when the electric motor 174 is actuated, thepulley and belt arrangement 176 will rotate the sleeve member 182. Sincethe arm member 170 is attached to sleeve 182, the arm member 170 willrotate and drive stop 156 along threaded surface 175 in an axialdirection. As the sleeve member 182 is rotated in a first direction, thearm member 170 will move the mechanical stop 156 to the left as viewedin FIG. 3, thereby increasing the maximum displacement of the pump 16.When the electric motor 174 is actuated to rotate the sleeve member 182in a second, opposite direction, the arm member 170 will move in anopposite axial direction, driving the mechanical stop member 156rightwardly, as viewed in FIG. 3, decreasing the maximum displacement ofthe pump 16.

The amount of movement of the adjustable mechanical stop 156, and thusthe amount of variation in the maximum displacement of the pump 16 isdetermined by the engagement of the pair of cam surfaces 198 and 199(FIG. 3) formed at the opposite ends of the stop 156, respectively, witha pair of limit switches 200 and 202 carried by the bracket assembly 168adjacent the stop member 156. The relative position of the limitswitches 200 and 202 with respect to the mechanical stop 156 may bepreset manually by set screws 203 extending through the switches andinto the bracket assembly 168. As the stop 156 moves in a directionwhich increases the maximum displacement position of the pump 16, thecam surface 198 will engage the limit switch 200 and deactivate theelectric motor 174, and when the stop 156 is moved in a direction whichdecreases the maximum displacement position, the cam surface 199 willengage the limit switch 202 to deactivate the electric motor 174.

Limit switches 200 and 202 form a portion of the electrical circuit 204,which is illustrated in FIG. 10 and used by an operator of the system 10for remotely controlling the electric motor 174 to selectively vary themaximum displacement of the pump 10 and thus the speed of the fluidcylinder 26.

The circuit 204 comprises a manually operated reversing drum switch 206having three portions; decrease,,off, and increase; the switch 206 beingused by the operator to selectively connect the electric motor 174 to anelectrical power supply 208. When the switch 206 is in the increaseposition, the electric motor 174 is activated in such a manner as torotate the arm member 170 to drive the stop 156 to increase the maximumdisplacement position. Engagement of the cam surface 198 with the limitswitch 200 deactivates the electric motor 174, thus limiting the maximumdisplacement of the pump 16 to a preset maximum limit. Thus the operatorof the fluid system 10 may increase the output speed of the systemwithout affecting its acceleration or deceleration characteristics and,without exceeding a predetermined maximum output speed. Likewise, ifthe operator of the system 10 wishes to decrease the maximumdisplacement position, the switch 206 is turned to the decreaseposition, wherein the power supply 208 is connected to the electricmotor 174 in such a manner so as to reverse its rotation and cause thearm member 170 to drive the stop 156 in an opposite direction todecrease the maximum displacement position. Engagement of the camsurface 199 of the stop 156 with the limit switch 202 breaks theelectrical connection between the electric motor 174 and the powersupply 208, thus limiting the maximum displacement position of the pump16 to a preset minimum limit. This variation in the maximum displacementof the pump 16 between maximum and minimum limits is determined by thespacing between the limit switches 200 and 202 and the spacing betweenthe cam surfaces 198 and 199, which is preset in any desired mannerdepending on the particular application of the fluid system 10. Itshould be noted that the minimum limit of the maximum displacementposition of the pump 16 cannot be less than the maximum preset minimumdisplacement position as determined by the mechanical stop 158.

Referring now to FIGS. 4-7, there is schematically illustrated a secondmodification of the pump 16 in which the secondary cylinder 46, theconnecting rod 140, the swash plate connecting arm 48, and theadjustable mechanical stops 156 and 158 are replaced by an internaldisplacement control mechanism generally indicated by the numeral 209.

The internal displacement control mechanism 209 comprises a pair ofdiametrically opposed piston members 210 and 212 respectively slidablymounted in intemal housing bores 214 and 216. The outer projecting endsof the pistons 210 and 212 are connected to the outer portions of theswash plate 44 by a suitable linkage 213 and rotate the swash plate 44in opposite directions about the axis 50 which is defined by thelongitudinal axes of trunnions 219 (FIG. 4A) on which the swash plate 44is rotatably mounted. The interior of the housing bores 214 and 216respectively form expansible pressure chambers 215 (FIG. 4) and 217(FIG. 5), which, in turn, are respectively connected to the conduits 126and 128, such that when fluid pressure is admitted into the pressurechamber 215 from the conduit 128,' the pressure therein generates aforce acting against the piston 210 to cause the swash plate 44 torotate toward a maximum displacement position; while, at the same time,the swash plate 44 displaces the piston 212 into the pressure chamber217 until the inner end of piston 212 abuts a mechanical stop 218. Theposition of the mechanical stop 218 determines the maximum displacementof the pump 16 in a manner similar to the mechanical stop 156 describedhereinbe fore. When it is desired to decrease the displacement of thepump 16, that is, when it is desired to rotate the swash plate 44 towarda minimum displacement position, fluid from the conduit 126 is directedintothe pressure chamber 217, wherein the pressure therewithin generatesa force acting against the piston 212 to cause the swash plate 44 torotate about the trunnions 219. The swash plate 44 will rotate towards sminimum displacement position driving the piston 210 into the bore 214until the inner end of the piston 210 abuts a manually adjustablemechanical stop 220. The manually adjustable stop 220 may take the formof a screw extending through the face of a pump 16 and into the pressurechamber 215, and is normally preset at any desired position andfunctions in a manner similar to the mechanical stop 158 describedherebefore. Suitable sealing means (not shown) prevents the passage offluid from the bore 214 y the stop 220 and externally of the pump 16. t

The mechanical stop 218, which controls the range of the maximumdisplacement of the pump 16 may be varied by an arm member 222 of anactuator 224 between a minimum and maximum limit. The actuator 224 issubstantially similar in function and structure to the actuator 172described hereinbefore, and is carried at the face of the pump 16 inaxial alignment with the bore 216. The arm member 222 of the actuator224 differs from the arm member in that the arm member 222 has a shearpin 192 with one end fixedly mounted in a bore 194 within the actuatorhousing 178, while the other end of the shear pin 192 is received in alongitudinal slot 196 that extends axially through the threaded sectionof the arm member 222. The shear pin 192, in addition to preventingdamage to the actuator 224 in the event the electric motor 174 is notdeactivated at the proper time, prevents relative rotary motion betweenthe arm member 222 and the sleeve 182 such that rotation of the sleeve182 produces axial movement of the arm member 222, which, in turn,produces axial movement of the stop 218 into the pres sure chamber 217.Suitable sealing means, such as an O-ring 234 within a peripheral recess235 in stop 218 prevents the passage of fluid thereby and into theactuator 224. I

It can thus be seen that when the electric motor 174 is activated in afirst direction by switch 206, the mechanical stop 218 will be drivenfrom the bore 216 (rightwardly as viewed in FIGS. 4 and 5) to increasethe maximum displacement position of the pump 16. By reversing therotation of the electric motor 174, the actuator 224 will drive themechanical stop 218 in an opposite direction, that is, into the bore 216to decrease the maximum displacement position of the pump 16 and thusdecreasing the output of the pump 16.

Since the limit switches 200 and 202 in the circuit 204 may not bepositioned proximate the stop 218, a feedback mechanism 236 (FIGS. 5, 6and 7) is provided to sense the position of the swash plate 44 andengage the limit switches 200 and 202, to control the rotation of theelectric motor 174 and define the limits in the variation of the maximumdisplacement position of pump 16. The feedback mechanism system 236 isillustrated in FIGS. 6 and 7 as comprising an outer housing 238 attachedto the pump 16 and including a longitudinal bore 239 in which aconnecting rod 240 is slidably mounted. One end of the connecting rod240 has a pair of cams 242 and 244 carried thereby, both cams having setscrews 247 for locking the cams to the connecting rod 240 to permittheir initial adjustment with respect to the limit switches 200 and 202.The other end of the connecting rod 240 is attached to a portion of theswash plate 44 by a pivotal linkage 248 such that as the swash plate 44is rotated about its trunnions 219 the linkage 248 will drive theconnecting rod 240 and thus the cams 242 and 244 relative to the limitswitches 200 and 202. Thus, when the pump 16 is at an intermediatemaximum displacement position and the operator of the fluid system 10desires to increase the displacement of the pump 16 and the speed of thefluid motor 26, the switch 206 is activated to cause the electric motor174 to drive the actuator 224 which, in turn,

causes the stop 218 to be moved from the bore 216 (rightwardly as viewedin FIGS. 4 and and thus permitting the piston 212 to move further intothe pressure chamber 217 under the force of the piston 210 actingagainst the opposite portion of the swash plate 44. The swash plate 44will rotate to increase the displacement of the pump 16 until the piston212 abuts the mechanical stop 218 which, in turn, is positioned when theelectric motor 174 is stopped by the limit switch 200 being engaged bythe cam 242 thereby positioning the stop 218 at a predetermined maximumlimit in a manner similar to that hereinbefore described in thedescription of the operation of the embodiment of FIG. 2. In a likemanner, when the operator of the system wishes to decrease the maximumdisplacement of the pump 16 and the speed of the fluid motor 26, theelectric motor 174 is activated by the switch 206 to rotate the actuator224 to drive the stop 218 into the bore 216 (leftwardly as viewed inFIGS. 4 and 5), causing the piston 212 to rotate the swash plate 44 todecrease the pump displacement. As the swash plate 44 is moving toward adecrease displacement, the cam 244 will engage the limit switch 202 todeactivate the electric motor 174, thereby positioning the stop 218 at apredetermined minimum limit. Thus, the maximum displacement of the pump16 may be varied by remote control within preset limits by varying theposition of the stop 218; those limits, in turn, being remotelycontrolled by en gagement of the cams 242 and 244 with the limitswitches 200 and 202, respectively, without having to change the rate ofacceleration or deceleration of the pump 16 and thus without having tochange the rate of acceleration or deceleration of the fluid motor 26.

Referring now to FIGS. 8 and 9 wherein there is schematicallyillustrated a third embodiment of the present invention in which thepump 16 of FIG. 2 is modified in a manner similar to the embodimentillustrated in FIG. 4, that is, an internal means 249 is provided forvarying the inclination of the swash plate 44 and thus the displacementof the pump 16. In the embodiment illustrated in FIG. 8, the swash plate44 rotates about a pair of pintle shafts 166 and 164 in the same manneras disclosed in FIG. 2, such that the pintle shaft 164 is easilyaccessible through the wall of the pump housing 30. As can best be seenin FIG. 9, a pair of cams 250 and 252 are attached by set screw 253 tothe end of the pintle shaft 164 and rotate therewith as the swash plate44 is rotated by the internal displacement control mechanism 249. Aplate 254 is attached to the end of the pintle shaft 164 below the cams250 and 252 and provides a means of initially adjusting the cams withrespect to the limit switches 200 and 202. The adjustment of theposition of the earn 250 and 252 may taken the form of set screws 256extending through elongated slots 258 in each cam and into threadedbores (not shown) formed in the plate 254. The limit switches 200 and202, mounted on plates 260 and 262, respectively, adjacent the cams 252and 250, are actuated by engagement with the cams 252 and 250 to breakthe connection between the electric motor 174 and the power supply 208when the swash plate 44 is rotated past defined limits in the samemanner as described hereinbefore. Initial adjustment of the position ofthe limit switches 200 and 202 is obtained by the relative positioningof elongated slots 264 in plates 260 and 262 with respect to screws 266passing through slots 264 into the wall of the pump housing 30.

The internal displacement mechanism 249 illustrated in FIG. 8 differsfrom the displacement mechanism 209 illustrated in FIG. 4 in that thedisplacement mechanism 249 comprises a pair of pistons 268 and 270 eachhaving one end respectively disposed in housing bores 272 and 274, withthe piston 270 having approximately twice the effective pressureresponsive areas as the piston 268, while the other ends of the pistons268 and 270 abut the swash plate in diametrically opposed locations.Stop 218 abuts the inner end of piston 270 and functions in the samemanner as hereinbefore described. The system 10 is also modified toaccommodate the displacement control mechanism 249 in that the bore 272is in constant communication with fluid pressure generating a force onpiston 268 urging the swash plate 44 toward a maximum displacementposition. When it is desired to stroke the swash plate 44 to maximumdisplacement position, fluid is metered-out from the bore 274 and whenit is desired to stroke the swash plate 44 to a minimum displacementposition fluid is metered-in to the bore 274. Since the area of thepiston 270 is approximately twice that of the piston 268, the swashplate 44 will be stroked to a minimum displacement position.

Further, in the embodiment disclosed in FIG. 4, the trunnions 219 are soconstructed that they are not accessible from the wall of the pumphousing 30, therefore it is necessary to have the pivot linkage 248 andthe connecting rod 240 to provide the feedback means 236 for controllingthe position of the stop 218; however, since the pintle shaft 164 in theembodiment illustrated in FIGS. 8 and 9 is easily accessible, such apivot linkage 248 and the connecting rod 240 is not required.

It can thus be seen that an improved fluid system has been provided forselectively starting, accelerating,.

decelerating, and stopping a fluid motor in which the maximum outputspeed of the fluid motor may be remotely selectively varied betweenpreset limits independent of the operating characteristics of thesystem.

While the forms of the embodiments of the present invention disclosedherein constitute preferred forms, it is to be understood that otherforms might be adopted all coming within the spirit of the invention andthe scope of the appended claims which follow.

What is claimed is as follows:

1. A fluid pressure energy translating device, comprising:

a housing having an inlet and an outlet port;

a cylinder barrel rotatably mounted within said housing, said cylinderbarrel having a plurality of arcuately spaced cylinder bores;

a plurality of pistons with inner ends disposed for reciprocal strokingmovement within said cylinder bores;

means for successively communicating said cylinder bores with said inletand outlet ports;

an inclined swash plate mounted in said housing in a drivingrelationship with the other end of said pistons for imparting saidreciprocal stroking movement to said pistons within said cylinder barrelbores as said cylinder barrel rotates, the amount of fluid flowing fromsaid inlet port to said outlet port being a function of the amount ofsaid reciprocal stroking movement of said pistons;

means for varying the inclination of said swash plate between selectedmaximum and minimum inclination positions to vary the amount of saidreciprocal stroking movement of said pistons such that the fluid flowingfrom said inlet port to said outlet port is increased as said swashplate inclination increases and said fluid flow between said inlet andoutlet ports decreases as said swash plate inclination is decreased;

a pair of stop means defining said maximum and minimum inclinationpositions;

electrically actuated means for selectively varying the position of oneof said stop means to vary one of said inclination positions betweenpreset limits;

a pair of spaced limit switch means electrically coupled to saidelectrically actuated means;

a pair of cam means respectively movable relative to said spaced limitswitch means for engagement therewith to terminate said electricallyactuated means when said one stop means has been moved to either of saidpreset limits. 4

2. The fluid pressure energy translating device defined in claim 1wherein said electrically actuated means is remotely controlled.

3. The fluid pressure energy translating device as defined in claim 1wherein said maximum inclination position as defined by one of said stopmeans is selectively varied between a higher preset limit and a lowerpreset limit by said electrically actuated means.

4. The fluid pressure energy translating device defined in claim 3wherein said lower limit of said maximum inclination position defined bysaid one stop means is greater than said minimum inclination positiondefined by said other stop means.

5. The fluid pressure energy translating device defined in claim 1wherein the means for varying the inclination of said swash platecomprises a connecting arm attached to said swash plate and extendingexternally of said housing, actuating means operatively coupled to saidconnecting arm and adapted to rotate said swash plate about apredetermined axis; said pair of stop means comprising a pair ofmechanical stops, one of which limits the amount of movement of saidswash plate in a first direction and defines said minimum inclinationposition, while the other of said mechanical stops limits the amount ofmovement of said swash plate in a second, opposite direction and definessaid maximum inclination position, one of said mechanical stops beingselectively varied between a higher preset limit and a lower presetlimit.

6. The fluid pressure energy translating device defined in claim 5wherein said cam means are carried by said one mechanical stop andadapted to engage said limit switch means to terminate said electricallyactuated means when said one mechanical stop is moved to either of saidpreset limits.

7. The fluid pressure energy translating device defined in claim 1wherein said swash plate is rotatable about a predetermined axis, afirst pressure responsive means carried within said housing adapted toengage said swash plate to rotate said swash plate about said axis tovary the inclination of said swash plate and thus the amount ofreciprocal stroking movement of said pistons within said cylinder bores,said first pressure responsive means tending to increase the inclinationof said swash plate; second pressure responsive means carried withinsaid housing and adapted to engage said swash plate to rotate said swashplate about said axis in an opposite direction to thereby decrease theinclination of said swash plate.

8. The fluid pressurev energy translating device defined in claim 7wherein said first pressure responsive means comprises a first pistonslidably mounted in a first pressure chamber in said housing and havingan extended end engaging said swash plate and adapted to extend underpressure from said pressure chamber to rotate said swash plate aboutsaid predetermined axis toward said maximum inclination position; saidsecond pressure responsive means comprising a second piston slidablymounted in a second pressure chamber, said second piston having anextended end engaging said swash plate and adapted to extend underpressure from said second pressure chamber to rotate said swash platetoward said minimum inclination position, said second pressure chamberhaving a movable mechanical stop disposed therein; and electricallyactuated means adapted to selectively move said mechanical stop towardand away from said second piston to limit the amount of inward movementof said second piston into said second pressure chamber, the movement ofsaid movable mechanical stop being defined by said preset limits.

9. The fluid pressure energy translating device defined in claim 8further comprising a movable rod member, said cams being carried on saidmovable rod member, and means connecting said rod member to said swashplate such that movement of said rod member isa function of therotational movement of said swash plate between said preset limits.

10. The fluid pressure energy translating device defined in claim 8wherein said swash plate is rotatably mounted on a pair of trunnionsextending from opposite sides of said swash plate and carried by saidhousing, one end of one of said trunnions being accessible through abore in said housing; said cam means being carried by said one end ofsaid one trunnion; said limit switch means being adapted to be engagedby said cam means when said swash plate is inclined to said limits suchthat said limit switch means terminates said electrically actuatedmeans.

1 l. A fluid system comprising:

a variable displacement pressure energy translating device having aninlet and an outlet;

pressure responsive means for varying the fluid displacement of saiddevice between selected minimum and maximum flow positions;

a pair of stop means defining said maximum and minimum flow positions;

. electrically actuated means for selectively varying the position ofone of said stop means to vary one of said flow positions betweenminimum and maximum limits;

a pair of spaced limit switch means electrically coupled to saidelectrically actuated means;

a pair of cam means respectively movable relative to said spaced limitswitch means for engagement therewith to terminate said electricallyactuated means when said one stop means has been moved to either of saidpreset limits;

fluid motor means operable in response to fluid pressure from saiddevice;

valve means for selectively connecting the inlet and the outlet of saiddevice to said fluid motor means;

a second source of fluid pressure; and

means for communicating said second source of fluid pressure to saidpressure responsive displacement varying means at a selected raTe tothereby vary the rate of change of the displacement of said fluidpressure energy translating device selectively between said maximum andminimum flow positlons.

12. The fluid system defined in claim 1 1 wherein said electricallyactuated means is remotely controlled.

13. The fluid system defined in claim 1 1 wherein said electricallyactuated means varies said maximum flow positions between said minimumand maximum limits.

14. The fluid system defined in claim 13 wherein said minimum limit ofsaid maximum flow position is greater than said selected minimum flowposition.

15. A fluid pressure energy translating device, comprising:

a housing having an inlet and an outlet port;

a cylinder barrel rotatably mounted within said housing, said cylinderbarrel having a plurality of arcuately spaced cylinder bores;

a plurality of pistons with inner ends disposed for reciprocal strokingmovement within said cylinder I bores;

means for successively communicating said cylinder bores with said inletand outlet ports;

an inclined swash plate mounted in said housing in a drivingrelationship with the other end of said pistons for imparting saidreciprocal stroking movement to said pistons within said cylinder barrelbores as said cylinder barrel rotates, the amount of fluid flowing fromsaid inlet port to said outlet port beinga function of the amount ofsaid reciprocal stroking movement of said pistons;

means for varying the inclination of said swash plate between selectedmaximum and minimum inclination positions to vary the amount of saidreciprocal stroking movement of said pistons such that the fluid flowingfrom said inlet port to said outlet port is increased as said swashplate inclination increases and said fluid flow between said inlet andoutlet ports decreases as said swash plate inclination is decreased,said means for varying the inclination of said swash plate comprising aconnecting arm attached to said swash plate and extending externally ofsaid housing;

actuating means operatively coupled to said conne cting arm and adaptedto rotate said swash plate about a predetermined axis;

a pair of mechanical stops, one of which limits the amount of movementof said swash plate in a first direction and defines said minimuminclination position, while the other of said mechanical stops limitsthe amount of movement of said swash plate in a second, oppositedirection and defines said maximum inclination position, one of saidmechanical stops being selectively varied between a higher preset limitand a lower preset limit, said maximum inclination position beingselectively variable between said higher and lower preset limits;

means for selectively varying said maximum inclination position betweensaid limits comprising electrically actuated means for moving said onemechanical stop;

limit switch means carried proximate said one mechanical stop; and

cam means carried by said one mechanical stop and adapted to engage saidlimit switch means to terminate said electrically actuated means whensaid one mechanical stop is moved to either of said preset limits.

16. A fluid pressure energy translating device, comprising:

a housing having an inlet and an outlet port;

a cylinder barrel rotatably mounted within said he using, said cylinderbarrel having a plurality of arcuately spaced cylinder bores;

a plurality of pistons with inner ends disposed for reciprocal strokingmovement within said cylinder bores;

means for successively communicating said cylinder bores with said inletand outlet ports;

an inclined swash plate mounted in said housing in a drivingrelationship with the other end of said pistons for imparting saidreciprocal stroking movement to said pistons within said cylinder barrelbores as said cylinder barrel rotates, the amount of fluid flowing fromsaid inlet port to said outlet port being a function of the amount ofsaid reciprocal stroking movement of said pistons;

means for varying the inclination of said swash plate between selectedmaximum and minimum inclination positions to vary the amount of saidreciprocal stroking movement of said pistons such that the fluid flowingfrom said inlet to said outlet port is increased as said swash plateinclination increases and said fluid flow between said inlet and outletports decreases as said swash plate inclination is decreased, said swashplate being rotatable about a predetermined axis;

a first pressure responsive means carried within said housing adapted toengage said swash plate to rotate said swash plate about said axis tovary the inclination of said swash plate and thus the amount ofreciprocal stroking movement of said pistons within said cylinder bores,said first pressure 7 responsive means tending to increase theinclination of said swash plate, said first pressure responsive meanscomprising a first piston slidably mounted in a first pressure chamberin said housingand having-an extended end engaging said swash plate andadapted to extend under pressure from said pressure chamber to rotatesaid swash plate about said predetermined axis toward said maximuminclination position;

second pressure responsive means carried within said Electricallyactuated means adapted to selectively move said mechanical stop towardand away from said second position to limit the amount of inwardmovement of said second piston into said second pressure chamber, themovement of said movable mechanical stop being defined by preset limits;

a pair of spaced limit switches; a

a pair of cams respectively adapted to engage said spaced limit switcheswhen said swash plate has been moved to said preset limits toterminatesaid electrically actuated means, said cams being carried on a movablerod member; and

means connecting said rod member to said swash plate such that movementof said rod member is a function of the rotational movement of saidswash plate between said preset 17. A fluid pressure energy translatingdevice, comprising:

a housing having an inlet and an outlet port;

means in said housing for displacing fluid between said ports;

means for varying the amount of fluid displaced by said device betweenselected minimum and maximum flow conditions;

a pair of stop means cooperating with said last mentioned means anddefining said maximum and minimum flow positions;

electrically actuated means for selectively varying the position of oneof said stop means to vary one of said flow positions between minimumand maximum limits;

a pair of spaced limit switch means electrically coupled to saidelectrically actuating means; and

a pair of cams respectively movable relative to said spaced limit switchmeans for engagement therewith to terminate said electrically actuatedmeans when said one stop means has been moved to either of said presetlimits.

1. A fluid pressure energy translating device, comprising: a housinghaving an inlet and an outlet port; a cylinder barrel rotatably mountedwithin said housing, said cylinder barrel having a plurality ofarcuately spaced cylinder bores; a plurality of pistons with inner endsdisposed for reciprocal stroking movement within said cylinder bores;means for successively communicating said cylinder bores with said inletand outlet ports; an inclined swash plate mounted in said housing in adriving relationship with the other end of said pistons for impartingsaid reciprocal stroking movement to said pistons within said cylinderbarrel bores as said cylinder barrel rotates, the amount of fluidflowing from said inlet port to said outlet port being a function of theamount of said reciprocal stroking movement of said pistons; means forvarying the inclination of said swash plate between selected maximum andminimum inclination positions to vary the amount of said reciprocalstroking movement of said pistons such that the fluid flowing from saidinlet port to said outlet port is increased as said swash plateinclination increases and said fluid flow between said inlet and outletports decreases as said swash plate inclination is decreased; a pair ofstop means defining said maximum and minimum inclination positions;electrically actuated means for selectively varying the position of oneof said stop means to vary one of said iNclination positions betweenpreset limits; a pair of spaced limit switch means electrically coupledto said electrically actuated means; a pair of cam means respectivelymovable relative to said spaced limit switch means for engagementtherewith to terminate said electrically actuated means when said onestop means has been moved to either of said preset limits.
 2. The fluidpressure energy translating device defined in claim 1 wherein saidelectrically actuated means is remotely controlled.
 3. The fluidpressure energy translating device as defined in claim 1 wherein saidmaximum inclination position as defined by one of said stop means isselectively varied between a higher preset limit and a lower presetlimit by said electrically actuated means.
 4. The fluid pressure energytranslating device defined in claim 3 wherein said lower limit of saidmaximum inclination position defined by said one stop means is greaterthan said minimum inclination position defined by said other stop means.5. The fluid pressure energy translating device defined in claim 1wherein the means for varying the inclination of said swash platecomprises a connecting arm attached to said swash plate and extendingexternally of said housing, actuating means operatively coupled to saidconnecting arm and adapted to rotate said swash plate about apredetermined axis; said pair of stop means comprising a pair ofmechanical stops, one of which limits the amount of movement of saidswash plate in a first direction and defines said minimum inclinationposition, while the other of said mechanical stops limits the amount ofmovement of said swash plate in a second, opposite direction and definessaid maximum inclination position, one of said mechanical stops beingselectively varied between a higher preset limit and a lower presetlimit.
 6. The fluid pressure energy translating device defined in claim5 wherein said cam means are carried by said one mechanical stop andadapted to engage said limit switch means to terminate said electricallyactuated means when said one mechanical stop is moved to either of saidpreset limits.
 7. The fluid pressure energy translating device definedin claim 1 wherein said swash plate is rotatable about a predeterminedaxis, a first pressure responsive means carried within said housingadapted to engage said swash plate to rotate said swash plate about saidaxis to vary the inclination of said swash plate and thus the amount ofreciprocal stroking movement of said pistons within said cylinder bores,said first pressure responsive means tending to increase the inclinationof said swash plate; second pressure responsive means carried withinsaid housing and adapted to engage said swash plate to rotate said swashplate about said axis in an opposite direction to thereby decrease theinclination of said swash plate.
 8. The fluid pressure energytranslating device defined in claim 7 wherein said first pressureresponsive means comprises a first piston slidably mounted in a firstpressure chamber in said housing and having an extended end engagingsaid swash plate and adapted to extend under pressure from said pressurechamber to rotate said swash plate about said predetermined axis towardsaid maximum inclination position; said second pressure responsive meanscomprising a second piston slidably mounted in a second pressurechamber, said second piston having an extended end engaging said swashplate and adapted to extend under pressure from said second pressurechamber to rotate said swash plate toward said minimum inclinationposition, said second pressure chamber having a movable mechanical stopdisposed therein; and electrically actuated means adapted to selectivelymove said mechanical stop toward and away from said second piston tolimit the amount of inward movement of said second piston into saidsecond pressure chamber, the movement of said movable mechanical stopbeing defined by said preset limits.
 9. The fluid pressure enerGytranslating device defined in claim 8 further comprising a movable rodmember, said cams being carried on said movable rod member, and meansconnecting said rod member to said swash plate such that movement ofsaid rod member is a function of the rotational movement of said swashplate between said preset limits.
 10. The fluid pressure energytranslating device defined in claim 8 wherein said swash plate isrotatably mounted on a pair of trunnions extending from opposite sidesof said swash plate and carried by said housing, one end of one of saidtrunnions being accessible through a bore in said housing; said cammeans being carried by said one end of said one trunnion; said limitswitch means being adapted to be engaged by said cam means when saidswash plate is inclined to said limits such that said limit switch meansterminates said electrically actuated means.
 11. A fluid systemcomprising: a variable displacement pressure energy translating devicehaving an inlet and an outlet; pressure responsive means for varying thefluid displacement of said device between selected minimum and maximumflow positions; a pair of stop means defining said maximum and minimumflow positions; electrically actuated means for selectively varying theposition of one of said stop means to vary one of said flow positionsbetween minimum and maximum limits; a pair of spaced limit switch meanselectrically coupled to said electrically actuated means; a pair of cammeans respectively movable relative to said spaced limit switch meansfor engagement therewith to terminate said electrically actuated meanswhen said one stop means has been moved to either of said preset limits;fluid motor means operable in response to fluid pressure from saiddevice; valve means for selectively connecting the inlet and the outletof said device to said fluid motor means; a second source of fluidpressure; and means for communicating said second source of fluidpressure to said pressure responsive displacement varying means at aselected raTe to thereby vary the rate of change of the displacement ofsaid fluid pressure energy translating device selectively between saidmaximum and minimum flow positions.
 12. The fluid system defined inclaim 11 wherein said electrically actuated means is remotelycontrolled.
 13. The fluid system defined in claim 11 wherein saidelectrically actuated means varies said maximum flow positions betweensaid minimum and maximum limits.
 14. The fluid system defined in claim13 wherein said minimum limit of said maximum flow position is greaterthan said selected minimum flow position.
 15. A fluid pressure energytranslating device, comprising: a housing having an inlet and an outletport; a cylinder barrel rotatably mounted within said housing, saidcylinder barrel having a plurality of arcuately spaced cylinder bores; aplurality of pistons with inner ends disposed for reciprocal strokingmovement within said cylinder bores; means for successivelycommunicating said cylinder bores with said inlet and outlet ports; aninclined swash plate mounted in said housing in a driving relationshipwith the other end of said pistons for imparting said reciprocalstroking movement to said pistons within said cylinder barrel bores assaid cylinder barrel rotates, the amount of fluid flowing from saidinlet port to said outlet port being a function of the amount of saidreciprocal stroking movement of said pistons; means for varying theinclination of said swash plate between selected maximum and minimuminclination positions to vary the amount of said reciprocal strokingmovement of said pistons such that the fluid flowing from said inletport to said outlet port is increased as said swash plate inclinationincreases and said fluid flow between said inlet and outlet portsdecreases as said swash plate inclination is decreased, said means forvarying the inclination of said swash plate comprisiNg a connecting armattached to said swash plate and extending externally of said housing;actuating means operatively coupled to said connecting arm and adaptedto rotate said swash plate about a predetermined axis; a pair ofmechanical stops, one of which limits the amount of movement of saidswash plate in a first direction and defines said minimum inclinationposition, while the other of said mechanical stops limits the amount ofmovement of said swash plate in a second, opposite direction and definessaid maximum inclination position, one of said mechanical stops beingselectively varied between a higher preset limit and a lower presetlimit, said maximum inclination position being selectively variablebetween said higher and lower preset limits; means for selectivelyvarying said maximum inclination position between said limits comprisingelectrically actuated means for moving said one mechanical stop; limitswitch means carried proximate said one mechanical stop; and cam meanscarried by said one mechanical stop and adapted to engage said limitswitch means to terminate said electrically actuated means when said onemechanical stop is moved to either of said preset limits.
 16. A fluidpressure energy translating device, comprising: a housing having aninlet and an outlet port; a cylinder barrel rotatably mounted withinsaid housing, said cylinder barrel having a plurality of arcuatelyspaced cylinder bores; a plurality of pistons with inner ends disposedfor reciprocal stroking movement within said cylinder bores; means forsuccessively communicating said cylinder bores with said inlet andoutlet ports; an inclined swash plate mounted in said housing in adriving relationship with the other end of said pistons for impartingsaid reciprocal stroking movement to said pistons within said cylinderbarrel bores as said cylinder barrel rotates, the amount of fluidflowing from said inlet port to said outlet port being a function of theamount of said reciprocal stroking movement of said pistons; means forvarying the inclination of said swash plate between selected maximum andminimum inclination positions to vary the amount of said reciprocalstroking movement of said pistons such that the fluid flowing from saidinlet to said outlet port is increased as said swash plate inclinationincreases and said fluid flow between said inlet and outlet portsdecreases as said swash plate inclination is decreased, said swash platebeing rotatable about a predetermined axis; a first pressure responsivemeans carried within said housing adapted to engage said swash plate torotate said swash plate about said axis to vary the inclination of saidswash plate and thus the amount of reciprocal stroking movement of saidpistons within said cylinder bores, said first pressure responsive meanstending to increase the inclination of said swash plate, said firstpressure responsive means comprising a first piston slidably mounted ina first pressure chamber in said housing and having an extended endengaging said swash plate and adapted to extend under pressure from saidpressure chamber to rotate said swash plate about said predeterminedaxis toward said maximum inclination position; second pressureresponsive means carried within said housing and adapted to engage saidswash plate to rotate said swash plate about said axis in an oppositedirection to thereby decrease the inclination of said swash plate, saidsecond pressure responsive means comprising a second piston slidablymounted in a second pressure chamber, said second piston having anextended end engaging said swash plate and adapted to extend underpressure from said second pressure chamber to rotate said swash platetoward said minimum inclination position, said second pressure chamberhaving a movable mechanical stop disposed therein; Electrically actuatedmeans adapted to selectively move said mechanical stop toward and awayfrom said second position to limit the aMount of inward movement of saidsecond piston into said second pressure chamber, the movement of saidmovable mechanical stop being defined by preset limits; a pair of spacedlimit switches; a pair of cams respectively adapted to engage saidspaced limit switches when said swash plate has been moved to saidpreset limits to terminate said electrically actuated means, said camsbeing carried on a movable rod member; and means connecting said rodmember to said swash plate such that movement of said rod member is afunction of the rotational movement of said swash plate between saidpreset limits.
 17. A fluid pressure energy translating device,comprising: a housing having an inlet and an outlet port; means in saidhousing for displacing fluid between said ports; means for varying theamount of fluid displaced by said device between selected minimum andmaximum flow conditions; a pair of stop means cooperating with said lastmentioned means and defining said maximum and minimum flow positions;electrically actuated means for selectively varying the position of oneof said stop means to vary one of said flow positions between minimumand maximum limits; a pair of spaced limit switch means electricallycoupled to said electrically actuating means; and a pair of camsrespectively movable relative to said spaced limit switch means forengagement therewith to terminate said electrically actuated means whensaid one stop means has been moved to either of said preset limits.